The determination of David Cameron to press ahead with legalising gay marriage opens up the possibility of a lesbian queen giving birth to a future monarch by artificial insemination, Lord Tebbit has warned.

Tebbit's remarks indicate that the marriage (same sex couples) bill will have a bumpy ride when it reaches the House of Lords.

Tebbit, who said that ministers have "fucked up" by alienating Tory grassroots, accused Downing Street of forcing through the legislation with little thought.

"The government discussed it for 20 minutes on the morning of its announcement," he told the Big Issue. "They'd done no work on it beforehand."

Tebbit also said he had challenged a minister about legalising gay marriage at the same time as ending male primogeniture in the royal succession.

"I said to a minister I know: have you thought this through? Because you're doing the law of succession, too.

"When we have a queen who is a lesbian and she marries another lady and then decides she would like to have a child and someone donates sperm and she gives birth to a child, is that child heir to the throne?"

Tebbit joked that the change could allow parents to marry their children as a way of avoiding inheritance tax. "It's like one of my colleagues said: we've got to make these same sex marriages available to all. It would lift my worries about inheritance tax because maybe I'd be allowed to marry my son. Why not? Why shouldn't a mother marry her daughter? Why shouldn't two elderly sisters living together marry each other?"

Lord Tebbit, who recently said he could understand why many people vote Ukip, said the party would attract greater financial support if they won the European parliamentary elections next year. He said: "If they make significant gains in the European elections, I know there's people rich enough to get involved and fund a significant campaign at a general election."